With the rapid development of touch panel technology, the touch panel technology has significant improvements and progress in aspects, such as product thickness, functions, etc., due to the influence and dictates of lightness, clearness, thinness, narrowness of electronic products and simplified input operations. Current resistive and capacitive touch panels can determine coordination positions on an X-Y plane through touch sensing, and realize touch input based on changes of coordination positions. With the continuous development, the current panels using single coordinate input cannot satisfy the versatile functional requirements of electronic devices. For instance, it can only sense plane positions of signals. This arrangement of the single signal input cannot fulfill the demand of the masses. For example, when multiplayers are operating, the signal inputs cannot be extended if the system only senses touch positions, and thus, the entertainment experience is significantly reduced.
In order to solve the above problem, the current solution is to add at least one electrode layer that is used for sensing the magnitude of pressure to the current touch panel. The capacitive pressure sensing principle is employed to determine the magnitude of pressing force. The capacitive pressure sensing method is to space apart the electrode layer a specific distance from a ground structure by using a support structure so as to form two capacitor plates. After being pressed by an external force, the distance between the two capacitive plates is decreased, and thus a capacitance value change is sensed by the electrode layer. A control system then senses the magnitude of the pressure according to the change in the capacitance value. The only insufficiency is that the capacitive pressure sensing principle is used for sensing deformations of the two capacitive plates, and the deformations are macro changes and have a larger influence range. When a finger touches one or more positions, points in its vicinity will also be affected to generate obvious changes in capacitances. The recognition rate of capacitive pressure sensing is therefore lower, and the accurate sensing of multi-finger force touch cannot be achieved.
Reference is now made to FIG. 1A, which is illustrated with the current capacitive sensing electrodes. The capacitive sensing principle in FIG. 1A is that: a distance d, between a first sensing electrode 101 and a second sensing electrode 102, is varied when the first sensing electrode 101 and the second sensing electrode 102 are depressed by a pressing force F. As a result, a further change is present in a capacitance value between the first sensing electrode 101 and the second sensing electrode 102. An amount of a capacitance value change between the two electrodes is positively correlated with a change amount of d. A magnitude of the pressing force F can thus be detected according to the amount of the capacitance value change to realize the force touch function.
Reference is now made to FIG. 1B. A force touch panel 100 having capacitive pressure sensing electrodes is provided. An X-Y coordinate system is provided. When an object (such as a finger) presses position A (or position B) of the force touch panel 100 shown in FIG. 1, the pressing force allows the distance d between the first sensing electrode 101 and the second sensing electrode 102 of the force touch panel 100 to change. The change of the distance d between the first sensing electrode 101 and the second sensing electrode 102 (that is, deformation) is a macro shape change, which affects a wide range and has more influences on adjacent positions.
For example, when a pressing force F presses position A (or position B), a capacitance at position A (or position B) changes, and a capacitance at a position adjacent to position A (or position B) subsequently changes obviously. It is thus difficult to distinguish whether pressing actions having different forces have respectively occurred at the two adjacent positions or only one pressing action has occurred. Even more, when forces are simultaneously exerted on two adjacent points, center of gravity possibly deviates so that the extents of deformations affect each other. The deformed positions and deformation extents thus cannot be accurately determined. Hence, the current capacitive pressure sensing electrode can only accurately identify one pressure.
Deformation extents of position A and position B of the force touch panel 100 shown in FIG. 1B after being applied by pressing forces and deformation extents of other adjacent positions are presented in Table 1A and Table 1B. X direction, Y direction, and a diagonal direction of the force touch panel 100 serve as examples in the tables for illustrating affected paths of positions adjacent to positions being pressed by the pressing forces, and distances between press positions and an edge (such as a bezel) of the force touch panel 100 along the above three direction are equally divided into positions (such as a first position, a second position, etc.). The deformation extents (changes of capacitance values are measurement criteria) are represented by percentages, and the deformation extents at the press positions are set as 100%.
TABLE 1AThe relational table of changes of deformation extents(capacitance values) after position A is pressed bya pressing force in capacitive pressure sensing.Press1st2nd3rd4th5thItemPositionPositionPositionPositionPositionPositionX Direction100%96%77%54%28%8%(a1)Y Direction100%97%86%66%42%11% (a2)Diagonal100%91%62%30% 5%0%Direction(a3)
TABLE 1BThe relational table of changes of deformation extents(capacitance values) after position B is pressed bya pressing force in capacitive pressure sensing.Press1st2nd3rd4th5thItemPositionPositionPositionPositionPositionPositionX Direction100%40%18%9%3%0%(b1)Y Direction100%71%44%9%3%0%(b2)Diagonal100%94%35%12% 3%0%Direction(b3)
As can be seen from Table 1A and Table 1B, when a finger presses position A and position B, influences on the positions adjacent to the press positions (such as the first position along X direction, Y direction, or the diagonal direction) by the pressing forces are greater in the capacitive pressure sensing according to the prior art. As shown in Table 1A, when position A is the press position, the deformation extents of the positions adjacent to position A along X direction, Y direction, and the diagonal direction are roughly equivalent to the deformation extents of position A (the difference is less than about 10%). Hence, distinctness cannot be effectively achieved. As shown in Table 1B, when position B is the press position, at a minimum the deformation extent of the position adjacent to position B along the diagonal direction is roughly equivalent to the deformation extent of position B. It is thus understood that the prior art multi-touch sensing method cannot effectively distinguish the press position from the adjacent position along at least one direction when the press positions are position A and position B.
Reference is now made to FIG. 2A to FIG. 2D. FIG. 2A to FIG. 2D are curves indicating relation between a distance between press positions by two fingers and a pressing signal change after applying pressing forces having the same magnitude, by two fingers, to the force touch panel 100. In the figures, the abscissa is the distance between the press positions by the two fingers, and the ordinate is the pressing signal change. The pressing signal change is a change of signal, such as resistance, voltage, or current. FIG. 2A to FIG. 2D respectively indicate that the distances between the press positions by the two fingers are 10 mm, 20 mm, 30 mm, and 60 mm. The press positions by the two fingers sense the pressing signal changes and there are no obvious peak resistance values because of the pressing forces. The signal change caused by two-finger press cannot be effectively distinguished. Hence, it is not easy for the prior art capacitive array pressure sensing method to achieve accurate multi-force sensing.
For the forgoing reasons, there is a need to solve the above-mentioned problems by providing a multi-force touch sensing method and a multi-force touch module.